The present invention relates to annular or tubular markers for catheters and to preferred production methods.
Markers are used for easier location of catheters in human or animal bodies and for this reason are generally opaque to X-rays. In this way, catheters or vessel supporting devices (stents), which are becoming smaller and smaller, can be more easily located. Typical markers have an outer diameter of approximately 100 to 600 μm, an inner diameter of approximately 40 to 500 μm, and a length of 0.5 to 2 mm.
From International application publication WO 2007/140635 A1, the use of markers for determining the position of catheters is known. In the distal end region of the catheters sit one or more radio-opaque, in, particular X-ray-opaque, sleeve-like markers on the wire shaft, which have essentially two functions. First, when the catheter is being used, the position of the guide wire tip should be easily recognizable in an X-ray imaging device—for example by an elongated marker coil directly on the distal end of the guide wire. Second, with the help of several markers arranged, for example, equidistant in front of the distal end, a length measurement of a stenosis to be treated could be performed on the X-ray imaging device. For this purpose, the markers must have an X-ray-opaque material, in order to achieve outstanding X-ray visibility. With known catheter guidance wires, there is the problem that, on the one hand, the wire should be as flexible as possible particularly on its distal end, in order to guarantee the most atraumatic insertion of the wire as possible into heart vessels and thereby an easy passage through narrow points and bends in the vessel course to be traversed.
Preferably, markers are placed on the catheters as rings or tubules. Such rings or tubules are cut from a long tube. Consequently, however, the dimensions are also limited. In order to achieve markers with smaller dimensions, small bands are placed around the catheters, whose mounting is, however, complicated as a result.
From the state of the art it is known to produce such markers either by drawing or cutting lengths of tubes or fusing foils. Fusing foils has proven to be disadvantageous, in particular because the fused connection is produced only unreliably. Cutting lengths of tubes comes up against mechanically feasible limits for wall thicknesses of less than 30 μm. Such types of production-limited wall thicknesses, however, run diametrically counter to the requirement for the thinnest possible diameter of the distal end of the catheter.
According to European published patent application EP 1 813 367 A2, markers are alternatively formed by metal injection. For this purpose, the X-ray-opaque metals are dispersed in the melt.